The invention relates to the fabrication of shallow-junction integrated devices and, more particularly, to the formation of reliable metal-to-junction contacts in such devices.
A variety of large-scale-integrated (LSI) devices of practical importance include very shallow junctions. For example, in some so-called short-channel metal-oxide-semiconductor (MOS) LSI devices, junction depths are reduced to submicron values in order to minimize overlap capacitance between the gate electrodes and their associated source-drain junction regions. But, as junctions become shallower, the likelihood increases that metals included in contact window portions of the device to make electrical connections to the junction regions will penetrate or spike through the junctions during sintering. In practice, metals such as aluminum have been known to penetrate junctions whose depths are less than one micron.
Various schemes have been proposed to minimize the occurrence of the aforedescribed spiking problem in shallow-junction LSI devices. Some proposals involve relatively elaborate metallization systems. These are often not attractive, however, because of the additional processing complexity they entail.
Another solution to the specified problem is described in U.S. Pat. No. 3,747,203. As shown for example, in FIGS. 8 through 10 thereof, that solution involves first forming a relatively deep central junction region. Thereafter, relatively shallow lateral extensions of the deep region are formed. But, if that technique is applied to the fabrication of conventional LSI devices, it will require a subsequent masking step to open contact windows in an additional insulating layer that would typically be deposited on top of the structure depicted in FIG. 10 of U.S. Pat. No. 3,747,203. Moreover, aligning such subsequently formed contact windows with respect to the deep junction regions is in practice a formidable problem. Unless precise alignment therebetween is achieved, the windows may overlie some part of the shallow lateral extensions of the junctions. In that case, penetration of the shallow extensions by the metallic contact material might occur.
Accordingly, continuing efforts have been directed at trying to devise simple and reliable techniques for making metal-to-junction contacts in shallow-junction LSI devices. It was recognized that such techniques if available would significantly advance the art of making such devices.